1. Field of the Invention
The present invention relates generally to waterproof/breathable ("WPB") fabric coatings and laminates. More specifically, the present invention relates to fire-resistant, WPB fabric coatings and laminates which minimize the risk of toxic compound production when exposed to flame or other high heat source.
2. Description of the Related Art
The markets for and uses of waterproof/breathable ("WPB") fabrics have greatly expanded since the development of Gore-Tex.RTM. and similar laminates. The advantages of WPB fabrics is their ability simultaneously to repel liquid water (waterproof) and permit the passage of water vapor (breathable). In practical terms, one wearing a WPB rain garment in inclement weather, even while exercising, would stay dry because the rain is kept out but perspiration evaporates away. This is a great improvement over fabrics which are waterproof but not breathable (e.g. polyurethane coated fabrics or polyvinyl chloride films) or breathable but not waterproof (e.g. cotton). The application of silicone or fluorocarbon or other water repellant to a breathable fabric (e.g. cotton) might provide some minimal water repellency, but falls far short of the performance of WPB fabrics.
Hydrophobic membranes are ideal candidates for use in WPB fabrics. The hydrophobic membrane contains very small pores that resist the entry of liquid water even at substantial pressures or when rubbed or flexed, but readily allow the flow of gases like water vapor. This is to be contrasted with wicking materials. Wicking materials are hydrophilic and porous with pores that interconnect to make complete pathways through the material. Liquid water moves through these materials by capillary action. While wicking materials easily transport water and water vapor from an internal to an external side, they offer no resistance to the entry of liquid water. Gore describes the use of hydrophobic layers in WPB fabrics in U.S. Pat. No. 3,953,566.
An example of a membrane for a WPB fabric is detailed in Gore et al., U.S. Pat. No. 4,194,041, where the membrane is a microporous polytetrafluoroethylene ("PTFE") laminate that possesses a high moisture vapor transmission rate even under adverse climatic conditions. This invention comprises a first layer of hydrophobic material attached to a second layer of hydrophilic material. A waterproof/breathable fabric is constructed by attaching this membrane to a suitable base fabric such as nylon taffeta. The hydrophobic layer prevents the entry of liquid water into the fabric, while the hydrophilic layer draws the interior moisture to the membrane so that it might evaporate through. Importantly, the hydrophilic layer also serves to prevent oils and contaminates in perspiration from entering the hydrophobic layer, coating its interior surfaces, and greatly reducing its ability to repel water. The Gore-Tex.RTM. membrane is available commercially from W. L. Gore & Associates, Inc.
Performance fabric technology incorporating WPB membranes has continued to advance rapidly. Gohlke, U.S. Pat. No. 4,344,999, developed a breathable laminate that serves as a bacteria barrier for hospital applications. Worden details a process for making stretchable Gore-Tex.RTM. membranes in U.S. Pat. No. 4,443,511. An anti-static WPB fabric for covering aerospace equipment was described by Saville et al. in U.S. Pat. No. 4,816,328. In U.S. Pat. No. 4,868,928, Norvell described a stretchable WPB garment for active outdoor gear. An improved Gore-Tex.RTM. membrane allowing for a greater water vapor transmission rate was described by Henn in U.S. Pat. No. 4,969,998. Wu, in U.S. Pat. No. 5,242,747, describes the use of oleophobic material in a WPB membrane to prevent damage and clogging from oils.
Generally speaking, there are two types of performance fabrics which exhibit WPB and windproof qualities: laminates and coated fabrics. Coated fabrics are created by applying rubber, PVC, polyurethane, ceramic or amino acid compounds to a fabric with a spray or bath or other method. In contrast, laminates are produced by sticking one or more membranes to a fabric via heat sealing or adhesives.
The Gore-Tex.RTM. membrane is generally laminated to a high performance fabric to create a laminated fabric. Some constructions even sandwich the Gore-Tex.RTM. membrane between two fabrics for additional comfort in wearing as personal garment. In general, these laminated fabrics are able to withstand very high water pressure (up to 65 psi) with minimal leakage, but "breathe" as water vapor passes through the fabric/membrane away from the body. This feature is due to the billions of microscopic pores in the membrane which are small enough to restrict water droplets but large enough to allow water vapor passage. One common Gore-Tex.RTM. membrane is a composite of a hydrophobic (water-hating) material into which is integrated an oleophobic (oil-hating) substance. The hydrophobic material prevents water droplets from penetrating the fabric. While allowing moisture vapor to pass through, the oleophobic material prevents penetration of contaminates like oils, insect repellents, and food.
Such a membrane is comprised of a rubbery or elastomeric binder (hydrophobic) and a polymeric filler of micron-sized particles (oleophobic). Alone, the rubbery material blocks the penetration of water; minuscule pathways are created by the addition of the polymer which allow for the passage of water vapor. The resulting membrane is ideal for use in WPB fabrics.
However, a significant problem arises with these WPB laminates. They often employ natural or synthetic rubbers in combination with a fluorinated polymer, e.g. Teflon.RTM.. When exposed to a high heat source or flame, the rubbery portion of this combination can burn and generate toxic by-products. The fluorocarbons also have the tendency to decompose in fire to produce toxic compounds.
Some have attempted to make WPB fabrics fire-resistant by applying a flame-retardant composition to the fabric (see U.S. Pat. No. 4,223,066). This method is deficient because of the tendency of the surface coatings to wash off during cleaning. Sun, in U.S. Pat. No. 5,418,054, details a fire-resistant WPB laminate comprised of two layers of expanded PTFE sealed together with a phosphorous-containing poly(urea-urethane) adhesive. While retaining its fire-resistant qualities even through cleaning or laundering, this invention does not address the danger of toxic compound production.
There is an ever present need for new, improved WPB laminates for high performance fabrics which are fire resistant and either do not present or significantly reduce the danger of toxic compound production. In particular, there is a need for such WPB laminates for fabrics to be used in industrial, military, commercial and emergency situations. Specifically, military tents and gear and shoes, airplane seat covers, clothing for fire-fighters or industrial workers exposed to high heat sources, and commercial fabrics for tents or roofs require waterproof, breatheable, fire-resistant and safety qualities. Laminates in the available art have been unable to provide the improved fire-resistant and safety features required by the described applications.